A glass plate has been used in view of high thermal stability, high transparency, or low moisture permeability, as a substrate for an electronic display such as a liquid crystal display, an organic electroluminescence display, a plasma display or an electronic paper or as a substrate of a photo-electronic device such as CCD or a CMOS sensor, or a solar battery. In recent years, as a cellular phone or portable information terminal units spread, use of a substrate which is flexible, light and difficult to be damaged, has been sought in place for a glass plate, which is relatively heavy and easy to be damaged.
Further, in a substrate for the electronic display element such as a liquid crystal display element, an organic electroluminescence display element, a plasma display, an electronic paper or touch panel or in a sealing material to protect the electronic display element from atmospheric air (moisture or oxygen) and elongate life of the electronic display element, use of a transparent film which is flexible, light and difficult to be damaged, has been sought in place for a glass plate, which is relatively heavy and easy to be damaged. Various studies of the transparent resin film have been made.
An inexpensive and versatile transparent resin film is disclosed. For example, an acrylate cross-linked resin is disclosed in Japanese Patent O.P.I. Publication No. 10-71667, a meleimide cross-linked resin in Japanese Patent O.P.I. Publication No. 5-209057, an α-methylstyrene cross-linked resin in Japanese Patent O.P.I. Publication No. 8-15682, a polycarbonate cross-linked resin in Japanese Patent O.P.I. Publication No. 2002-173529, and an epoxy cross-linked resin in Japanese Patent O.P.I. Publication No. 2001-59015. Further, polyethersulfone-polyacrylate plate laminate disclosed in Japanese Patent O.P.I. Publication No. 5-142525, polyethersulfone, or polycarbonate has been proposed, and some of them have been put into practical use.
In an electronic device such as a liquid crystal display, an organic EL display and a touch panel, an element of the electronic device is provided on a transparent film as a plastic substrate, and a transparent film as a sealing material is provided on the resulting material so as to protect the element from moisture or oxygen in atmosphere, the two films being adhered to each other through an adhesive.
As the adhesive, a UV curable resin is mainly used. A sealing material is superposed on a substrate, and the adhesive is applied between the substrate and the sealing material. Thereafter, the superposed material is subjected to actinic light (UV light) exposure from for example, the sealing material to cure the adhesive and form a sealed structure (sealing treatment).
Hitherto, a glass plate, having a good moisture resistance, has been mainly used as the substrate of the electronic display element or the sealing material. The glass plate has no problem during sealing treatment.
When a transparent resin film is used in place for the glass plate, it has been found that a PET film, a PEN film, or the polyethersulfone film described above has problem in sealing treatment in which curing of a UV curable resin constituting an adhesive does not sufficiently proceed on UV exposure, and has further problem in that thermal shrinkage or thermal deterioration occurs due to heat radiation to the film from a light source and due to heat generation of the film itself by UV absorption. The norbornene film, although there is no problem of curing of a UV curable resin, is made brittle upon UV exposure.
As is described above, a glass plate as the substrate or the sealing material cannot be simply substituted with any transparent resin film.
Further, it is necessary for a transparent resin film used for the electronic display to have characteristics such as an optical property, for example, birefringence and a gas barrier property. A transparent resin film having all of these necessary characteristics is not known.